Mechanical grate



Feb. 7, i967 A. GoDEl.

MECHANICAL GRATE Filed July 12, 1965 IVI/l NVENTOR.

LBE/Z T GDEL BY y u A 7' TQQ/VE Y United States Patent 1 claim. (ci. 11o-40) This invention relates to a mechanical grate and refers more particularly to mechanical grates having the shape of endless chains and used for the combustion of a duidized bed of granulated or pulverulent combustible substances as described in U.S. Patent No. 2,866,696.

The combustion of a fluidized bed has the advantage of producing combustion rates which are very high per unit of the grate surface; often they are eight to ten times higher than those of usual grates wherein combustion takes place in a static layer. However, the speed of movement of the grate must be very greatly increased to assure satisfactory removal of ashes.

This fact creates a particularly acute problem of premature wear out of the material, particularly in case of endless grates with stretched chains extending horizontally or at an inclination, which are now used in industrial practice in order to burn combustibles in a uidized bed.

An object of the present invention is to eliminate the above-mentioned drawbacks.

Another object is to provide a novel and improved construction of a mechanical grate having the shape of an endless chain.

Other objects of the present invention will become apparent in the course of the following specification.

In the accomplishment of the objectives of the present invention it was found desirable to provide a mechanical grate shaped as an endless chain located between two rollers and comprising an upper section supported by slides and a lower freely hanging section. The grate is associated with supporting partitions for the blowing of the air of uidization, which are located in an air chamber and provided with ventilation aps for regulating the supply of the blown air, and which are located just below the upper section of the grate but without extending to the lower hanging section. By freeing in this manner the lower grate section from all contact with the zone of blown air, it is possible to simplify the construction of the grate and reduce the wear and tear caused by friction of the lower grate section with air-tight seals andV with the bottom of the air transmitting partitions.

The invenion will appear more clearly from the following detailed description when taken in connection with the accompanying drawing, showing by way of example, preferred embodiments of the inventive idea.

In the drawing:

FIGURE l is a diagrammatic sectional side view of a furnace provided with an inclined mechanical grate shaped as a hanging chain in accordance with the present invention, for the combustion of a uidized bed.

FIGURE 2 is a transverse section along the line II-II of FIG. 1 and shows air transmitting means, including a sleeve containing air-regulating means, and an air distributing duct.

FIGURE 3 is similar to FIG. 2 but shows a somewhat different construction.

FIGS. 1 and 2 show a mechanical grate of the present invention which comprises an endless grate sheet 1 consisting of longitudinal bars joined by transverse pivotal connections and forming a hanging chain extending over rollers 2 and 3 which are located at different heights and which are carried by supports 4, 5, respectively, fixed upon the bottom of the furnace. One of the rollers, such ice as the roller 3, is driven by a variable speed motor not shown in the drawing; the other roller 2 is freely rotatably mounted. Thus the upper portion of the grate 1 which extends at a suitable inclination, for example, of about 12 degrees, is subject to continuous traction, while tension in the lower freely Vhanging portion of the grate is substantially constant. Furthermore, the upper p0rtion of the grate rests upon longitudinal slides 6 integral with two beams 7 and 8 which are U-shaped in crosssection and the ends of which are fixed upon supports 4, 5. These beams carry lateral chain guides 9, 10 which serve to guide the grate laterally and upon which are mounted pipes 11, 12 used for the circulation of water.

Partitions fixed under the beams form passages 13 for blowing the primary air of uidization at a pressure differential varying according to the depth of the fluidized bed. Air is supplied by sleeves 14 provided with regulating flaps 15 and connected to an inclined conduit 16 for distributing air.

The bottoms of partitioned passages 13 are inclined so as to facilitate the outflow of the sieved ridlings which passed through the grate, toward a tubular opening 17; this outflow may be furthered by directing air blown through the grate toward the opening 17. The sieved ridlings are evacuated through tubes 18, through which also passes air coming from the partitioned passages; the ridlings pass into a collecting bunker 19 while air finally escapes through a pipe 20 toward the ash-collecting shaft 21 of the furnace.

Furthermore, a pneumatic seal 22 having an air passage 22a is located at the front part of the grate (which is the left hand side of FIG. l); the passage 22a is maintained under pressure by air introduced into a pipe 23. The outward flow of air is prevented by a shoe 24 sliding upon the surface of the grate 1. The purpose of this pneumatic seal is to prevent the tluidized bed of combustibles, such as small combusted coal particles, from escaping outwardly; the bed is formed in the combustion charnber 25 over the upper section of the grate under action of air blown out of the partitioned passages 13. The combustibles are supplied through the charging hopper 26.

Furthermore, a pipe 27 which blows in air, assures the removal of dust from the layer of clinkers evacuated by the grate while pushing away unburned soot particles in the fluidized bed.

Lubricating means are supplied to the hanging portion ofthe chain as indicated at 30.

The operation is as follows:

The inclined grate is driven forwardly in the direction of the arrow f by the driving roller 3 and carries a combustible iluidized bed pneumatically injected by the charging hopper 26 into the combustion chamber 25. The bed is maintained in combustion in a iluidized state by primary air blown into the partitioned passages 13, the pressure of which is conveniently regulated by dampers 15 in each sleeve 14. Ashes decant in form of clinkers in the uidized bed and are carried by the grate to the rear of the furnace where they are dropped into the ash-collecting shaft 21.

A grate of this type can be used effectively in boiler furnaces, drier furnaces, etc.

There are many )advantages resulting from the use of a grate of the present invention forming a hanging chain.

Thus the use of partitioned passages located under the upper section of the hanging chain-like grate makes it possible to regulate the outflow of the blown air of fluidization at each point of the grate. With the exception of this upper section, no `other part of :the grate is subjected to the blown air and, therefore, it is not necessary to provide means for isolating the hanging section. Due to this arrangement, the hanging section of the gnate is completely free and accessible; thus it is not only easily possible to replace the damaged bars of the grate, but it is also possible to lubricate the grate, for example, by pulverizing colloidal graphite or -by coating the hanging section with bisulfite of molybdenum, as indicated at 30, by means located outside of the air chamber, out of reach of grit and dust blown by the action of air. This assures easy sliding without wear of the inner surfaces of the bars of the grate upon the slides and also upon the grate guides. This advantage is particularly appreciable when considering that the combustion of the uidized bed requires a comparatively quick forward movement of the grate and consequently, without lubrication the wear of its component parts would be effective.

Another advantage of the present invention resides in the economy in construction caused by the absence of any support or air chamber under the hanging section. FIGURE 3 shows a similar construction, wherein the bottoms of the partitioned sections 13 are inclined in opposite directions so that tubes 18 and sleeves 14 are located on opposite sides of these sections. This construction is particularly advantageous when the size of the grate is an important factor.

It is apparent that the above examples have been given solely lby way of illustration and not by way of limita tion and that they are subject to many other variations and modifications within the scope of the present invention. For example, that part of the upper section of the endless grate which is under the pneumatic seal and under the front portion of the furnace, may extend horizontally and then bend upwardly so as to constitute an ascending part extending toward the rear portion of the furnace.

The bars constituting the movable surface of the grate, on the other hand, can be provided with grooves upon their upper surfaces in engagement with clinkers so as to facilitate their removal. A

Also, the gnate surface can be formed by transverse tipping bars which are supported by an endless chain extending around the rollers; the grate can be pulled by the forwardly located roller; the partitioned passages can be supplied with air through their bottoms; Iand the screened ridlings particles can be recovered in each partitioned passage or in a collecting bunker by pneumatic suction and then again ejected into the furnace, or they can be collected hydraulically under each partitioned passage and then removed by drains.

All such and other Variations and modifications are to be included within the scope of the present invention.

What is claimed is:

In a furance having a front portion, a rear portion and a bottom, a support mounted upon said bottom in said front portion, a rotary roller carried by said support, another support -mounted upon said bottom in said rear portion, :another rotary roller carried by said other sup port and situated at a higher level than the rst-mentioned roller and extending parallel thereto, a mechanical grate consisting of an endless chain-like member extending over said two rollers and driven thereby, said grate having an upper section and a lower freely hanging section, beams carried by said supports, slides supporting said upper section and carried yby said beams, means carried by said beams and forming partitioned passages located close to and below said upper section and cornmunicating therewith, means supplying blowing air to said passages to form a uidized bed of combustible particles above said upper section land including means regulating said supply of air, said partitioned passages terminating above said lower freely hanging section, whereby said lower freely hanging section is devoid of contact with said partitioned passages, chain guides carried by said beams and laterally engaging said gnate, water-circulting pipes carried by said lateral chain guides, said partitioned passages having inclined bottoms, means located at the lower ends of said inclined bottoms for the removal of ridlings, a pneumatic seal located in said front portion and having means blowing lair under pressure upon the upper section of said grate adjacent the first-mentioned roller and a shoe sliding upon the surface of the moving upper section of said grate land located in front of said pneumatic seal to prevent the air blown by said pneumatic seal from escaping outwardly, said seal preventing the escape of the uidized bed, said rear -portion having an ash-collecting shaft adjacent the secondmentioned roller.

References Cited by the Examiner UNITED STATES PATENTS 2,302,173 l 1/ 1942 Beers 110-40 2,370,274 2/ 1945 VVallens 110-40 2,380,930 8/1945 Andersen et al. 110-40 2,488,689 ll/1949 Smith et al. -40 2,730,971 l/1956 Birkner 110-40 2,866,696 12/1958 Godel 48-203 FOREIGN PATENTS 792,764 4/1958 Great Britain.

KENNETH W. SPRAGUE, Primary Examiner. 

